The invention pertains to a particle comprising a composition containing a matrix and a peroxide or azo radical initiator. The invention further relates to a particle-elastomer composition, and to a skim product, a tire, a tire tread, an undertread, a belt, and a hose comprising said particle-elastomer composition.
In the tire and belt industry, among others, better mechanical, heat build up and hysteresis properties are being demanded. It has long been known that the mechanical properties of rubber can be improved by using a large amount of sulfur as a cross-linking agent to increase the crosslink density in vulcanized rubbers. However, the use of large amounts of sulfur suffers from the disadvantage of high heat generation that leads to a marked decrease in heat resistance and resistance to flex cracking, among other properties, in the final product. In order to eliminate the foregoing disadvantage, it was proposed to add treated chopped fiber, pellets made thereof or treated pellets, particularly treated with polysulfides, Bunte salt, and sulfur to sulfur-vulcanization systems. These pellets further contain wax to improve processing. Although there were improvements in e.g. hysteresis and flex cracking, these improvements were not found when uncured compounds were aged before vulcanization. This is a drawback in applications where uncured compounds are kept for a certain number of days. The present invention has among others to its object to provide particles that maintain their advantageous properties when used in uncured compounds.
Waxed pellets as such are known in the art. For instance, in EP 0 889 072 the coating of aramid pellets with a polymeric component, e.g. a wax, was disclosed. However, these pellets do not comprise a peroxide- or an azo-containing wax.
In U.S. Pat. No. 6,068,922 pellets comprising aramid fibers and an extrudable polymer, e.g. polyethylene, polypropylene or polyamides are disclosed. The fibers may be coated by typical sizing agents (RF, epoxy, silicone). Coatings containing radical initiators are not disclosed.